Network Layer (OSI)
The Internet Protocol (IP) is the most common protocol at layer 3. Subnets represent layer-3 networks.
Routers are a common piece of equipment at layer-3. They are responsible for passing traffic from one network to the next. They also find the best path to a destination network.
The Internet Protocol breaks information into manageable pieces of information called packets. The receiving device reassembles packets into the original information.